1 //! An "interner" is a data structure that associates values with usize tags and
2 //! allows bidirectional lookup; i.e., given a value, one can easily find the
3 //! type, and vice versa.
5 use rustc_arena::DroplessArena;
6 use rustc_data_structures::fx::FxHashMap;
7 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
8 use rustc_macros::HashStable_Generic;
9 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
11 use std::cmp::{Ord, PartialEq, PartialOrd};
13 use std::hash::{Hash, Hasher};
16 use crate::{Edition, Span, DUMMY_SP, SESSION_GLOBALS};
21 // The proc macro code for this is in `src/librustc_macros/src/symbols.rs`.
23 // After modifying this list adjust `is_special`, `is_used_keyword`/`is_unused_keyword`,
24 // this should be rarely necessary though if the keywords are kept in alphabetic order.
26 // Special reserved identifiers used internally for elided lifetimes,
27 // unnamed method parameters, crate root module, error recovery etc.
30 DollarCrate: "$crate",
33 // Keywords that are used in stable Rust.
70 // Keywords that are used in unstable Rust or reserved for future use.
84 // Edition-specific keywords that are used in stable Rust.
85 Async: "async", // >= 2018 Edition only
86 Await: "await", // >= 2018 Edition only
87 Dyn: "dyn", // >= 2018 Edition only
89 // Edition-specific keywords that are used in unstable Rust or reserved for future use.
90 Try: "try", // >= 2018 Edition only
92 // Special lifetime names
93 UnderscoreLifetime: "'_",
94 StaticLifetime: "'static",
96 // Weak keywords, have special meaning only in specific contexts.
100 MacroRules: "macro_rules",
105 // Pre-interned symbols that can be referred to with `rustc_span::sym::*`.
107 // The symbol is the stringified identifier unless otherwise specified, in
108 // which case the name should mention the non-identifier punctuation.
109 // E.g. `sym::proc_dash_macro` represents "proc-macro", and it shouldn't be
110 // called `sym::proc_macro` because then it's easy to mistakenly think it
111 // represents "proc_macro".
113 // As well as the symbols listed, there are symbols for the strings
114 // "0", "1", ..., "9", which are accessible via `sym::integer`.
116 // The proc macro will abort if symbols are not in alphabetical order (as
117 // defined by `impl Ord for str`) or if any symbols are duplicated. Vim
118 // users can sort the list by selecting it and executing the command
119 // `:'<,'>!LC_ALL=C sort`.
121 // There is currently no checking that all symbols are used; that would be
181 ProceduralMasqueradeDummyType,
219 aarch64_target_feature,
223 abi_c_cmse_nonsecure_call,
225 abi_msp430_interrupt,
238 advanced_slice_patterns,
253 allow_internal_unsafe,
254 allow_internal_unstable,
260 arbitrary_enum_discriminant,
261 arbitrary_self_types,
273 assert_receiver_is_total_eq,
277 associated_type_bounds,
278 associated_type_defaults,
289 augmented_assignments,
291 automatically_derived,
292 avx512_target_feature,
298 bind_by_move_pattern_guards,
309 borrowck_graphviz_format,
310 borrowck_graphviz_postflow,
311 borrowck_graphviz_preflow,
315 braced_empty_structs,
325 capture_disjoint_fields,
337 cfg_target_has_atomic,
338 cfg_target_thread_local,
348 closure_to_fn_coercion,
350 cmpxchg16b_target_feature,
351 cmse_nonsecure_entry,
359 conservative_impl_trait,
362 const_compare_raw_pointers,
365 const_evaluatable_checked,
368 const_fn_floating_point_arithmetic,
369 const_fn_fn_ptr_basics,
373 const_generics_defaults,
376 const_in_array_repeat_expressions,
382 const_precise_live_drops,
385 const_raw_ptr_to_usize_cast,
388 const_trait_bound_opt_out,
404 core_panic_2015_macro,
413 crate_visibility_modifier,
414 crt_dash_static: "crt-static",
423 custom_inner_attributes,
424 custom_test_frameworks,
438 default_alloc_error_handler,
439 default_lib_allocator,
440 default_type_parameter_fallback,
442 delay_span_bug_from_inside_query,
450 destructuring_assignment,
466 document_private_items,
467 dotdot_in_tuple_patterns,
468 dotdoteq_in_patterns,
476 dropck_parametricity,
485 emit_enum_variant_arg,
493 ermsb_target_feature,
498 exclusive_range_pattern,
499 exhaustive_integer_patterns,
510 extended_key_value_attributes,
511 extern_absolute_paths,
512 extern_crate_item_prelude,
534 field_init_shorthand,
539 float_to_int_unchecked,
566 from_size_align_unchecked,
579 generic_associated_types,
586 half_open_range_patterns,
588 hexagon_target_feature,
590 homogeneous_aggregate,
607 if_while_or_patterns,
609 impl_header_lifetime_elision,
612 impl_trait_in_bindings,
618 inclusive_range_syntax,
621 infer_outlives_requirements,
622 infer_static_outlives_requirements,
634 irrefutable_let_patterns,
638 issue_5723_bootstrap,
639 issue_tracker_base_url,
651 lazy_normalization_consts,
663 link_llvm_intrinsics,
682 macro_at_most_once_rep,
683 macro_attributes_in_derive_output,
686 macro_lifetime_matcher,
687 macro_literal_matcher,
699 match_beginning_vert,
700 match_default_bindings,
727 movbe_target_feature,
776 nontrapping_dash_fptoint: "nontrapping-fptoint",
781 object_safe_for_dispatch,
784 omit_gdb_pretty_printer_section,
793 optin_builtin_traits,
802 overlapping_marker_traits,
812 panic_implementation,
842 post_dash_lto: "post-lto",
843 powerpc_target_feature,
848 pre_dash_lto: "pre-lto",
849 precise_pointer_size_matching,
853 prefetch_read_instruction,
855 prefetch_write_instruction,
860 proc_dash_macro: "proc-macro",
862 proc_macro_attribute,
868 proc_macro_internals,
870 proc_macro_non_items,
871 proc_macro_path_invoc,
883 quad_precision_float,
890 re_rebalance_coherence,
893 read_enum_variant_arg,
901 reexport_test_harness_main,
914 relaxed_struct_unsize,
930 riscv_target_feature,
943 rust_eh_catch_typeinfo,
945 rust_eh_register_frames,
946 rust_eh_unregister_frames,
950 rustc_allocator_nounwind,
951 rustc_allow_const_fn_unstable,
952 rustc_args_required_const,
955 rustc_capture_analysis,
958 rustc_const_unstable,
959 rustc_conversion_suggestion,
962 rustc_diagnostic_item,
963 rustc_diagnostic_macros,
966 rustc_dump_env_program_clauses,
967 rustc_dump_program_clauses,
968 rustc_dump_user_substs,
970 rustc_expected_cgu_reuse,
971 rustc_if_this_changed,
972 rustc_inherit_overflow_checks,
974 rustc_layout_scalar_valid_range_end,
975 rustc_layout_scalar_valid_range_start,
976 rustc_macro_transparency,
978 rustc_nonnull_optimization_guaranteed,
979 rustc_object_lifetime_default,
980 rustc_on_unimplemented,
983 rustc_partition_codegened,
984 rustc_partition_reused,
986 rustc_peek_definite_init,
987 rustc_peek_indirectly_mutable,
989 rustc_peek_maybe_init,
990 rustc_peek_maybe_uninit,
991 rustc_polymorphize_error,
993 rustc_proc_macro_decls,
996 rustc_reservation_impl,
998 rustc_specialization_trait,
1000 rustc_std_internal_symbol,
1004 rustc_then_this_would_need,
1005 rustc_unsafe_specialization_marker,
1008 rvalue_static_promotion,
1056 simd_reduce_add_ordered,
1057 simd_reduce_add_unordered,
1062 simd_reduce_max_nanless,
1064 simd_reduce_min_nanless,
1065 simd_reduce_mul_ordered,
1066 simd_reduce_mul_unordered,
1070 simd_saturating_add,
1071 simd_saturating_sub,
1074 simd_select_bitmask,
1100 sse4a_target_feature,
1112 std_panic_2015_macro,
1115 stmt_expr_attributes,
1116 stop_after_dataflow,
1121 struct_field_attributes,
1143 target_has_atomic_equal_alignment,
1144 target_has_atomic_load_store,
1146 target_pointer_width,
1147 target_target_vendor,
1148 target_thread_local,
1154 termination_trait_test,
1157 test_accepted_feature,
1159 test_removed_feature,
1186 type_alias_enum_variants,
1187 type_alias_impl_trait,
1198 unaligned_volatile_load,
1199 unaligned_volatile_store,
1208 underscore_const_names,
1210 underscore_lifetimes,
1213 universal_impl_trait,
1220 unrestricted_attribute_tokens,
1221 unsafe_block_in_unsafe_fn,
1223 unsafe_no_drop_flag,
1227 unsized_tuple_coercion,
1230 unused_qualifications,
1252 visible_private_types,
1254 volatile_copy_memory,
1255 volatile_copy_nonoverlapping_memory,
1257 volatile_set_memory,
1263 wasm_target_feature,
1278 #[derive(Copy, Clone, Eq, HashStable_Generic, Encodable, Decodable)]
1286 /// Constructs a new identifier from a symbol and a span.
1287 pub const fn new(name: Symbol, span: Span) -> Ident {
1288 Ident { name, span }
1291 /// Constructs a new identifier with a dummy span.
1293 pub const fn with_dummy_span(name: Symbol) -> Ident {
1294 Ident::new(name, DUMMY_SP)
1298 pub fn invalid() -> Ident {
1299 Ident::with_dummy_span(kw::Empty)
1302 /// Maps a string to an identifier with a dummy span.
1303 pub fn from_str(string: &str) -> Ident {
1304 Ident::with_dummy_span(Symbol::intern(string))
1307 /// Maps a string and a span to an identifier.
1308 pub fn from_str_and_span(string: &str, span: Span) -> Ident {
1309 Ident::new(Symbol::intern(string), span)
1312 /// Replaces `lo` and `hi` with those from `span`, but keep hygiene context.
1313 pub fn with_span_pos(self, span: Span) -> Ident {
1314 Ident::new(self.name, span.with_ctxt(self.span.ctxt()))
1317 pub fn without_first_quote(self) -> Ident {
1318 Ident::new(Symbol::intern(self.as_str().trim_start_matches('\'')), self.span)
1321 /// "Normalize" ident for use in comparisons using "item hygiene".
1322 /// Identifiers with same string value become same if they came from the same macro 2.0 macro
1323 /// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
1324 /// different macro 2.0 macros.
1325 /// Technically, this operation strips all non-opaque marks from ident's syntactic context.
1326 pub fn normalize_to_macros_2_0(self) -> Ident {
1327 Ident::new(self.name, self.span.normalize_to_macros_2_0())
1330 /// "Normalize" ident for use in comparisons using "local variable hygiene".
1331 /// Identifiers with same string value become same if they came from the same non-transparent
1332 /// macro (e.g., `macro` or `macro_rules!` items) and stay different if they came from different
1333 /// non-transparent macros.
1334 /// Technically, this operation strips all transparent marks from ident's syntactic context.
1335 pub fn normalize_to_macro_rules(self) -> Ident {
1336 Ident::new(self.name, self.span.normalize_to_macro_rules())
1339 /// Convert the name to a `SymbolStr`. This is a slowish operation because
1340 /// it requires locking the symbol interner.
1341 pub fn as_str(self) -> SymbolStr {
1346 impl PartialEq for Ident {
1347 fn eq(&self, rhs: &Self) -> bool {
1348 self.name == rhs.name && self.span.ctxt() == rhs.span.ctxt()
1352 impl Hash for Ident {
1353 fn hash<H: Hasher>(&self, state: &mut H) {
1354 self.name.hash(state);
1355 self.span.ctxt().hash(state);
1359 impl fmt::Debug for Ident {
1360 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1361 fmt::Display::fmt(self, f)?;
1362 fmt::Debug::fmt(&self.span.ctxt(), f)
1366 /// This implementation is supposed to be used in error messages, so it's expected to be identical
1367 /// to printing the original identifier token written in source code (`token_to_string`),
1368 /// except that AST identifiers don't keep the rawness flag, so we have to guess it.
1369 impl fmt::Display for Ident {
1370 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1371 fmt::Display::fmt(&IdentPrinter::new(self.name, self.is_raw_guess(), None), f)
1375 /// This is the most general way to print identifiers.
1376 /// AST pretty-printer is used as a fallback for turning AST structures into token streams for
1377 /// proc macros. Additionally, proc macros may stringify their input and expect it survive the
1378 /// stringification (especially true for proc macro derives written between Rust 1.15 and 1.30).
1379 /// So we need to somehow pretty-print `$crate` in a way preserving at least some of its
1380 /// hygiene data, most importantly name of the crate it refers to.
1381 /// As a result we print `$crate` as `crate` if it refers to the local crate
1382 /// and as `::other_crate_name` if it refers to some other crate.
1383 /// Note, that this is only done if the ident token is printed from inside of AST pretty-pringing,
1384 /// but not otherwise. Pretty-printing is the only way for proc macros to discover token contents,
1385 /// so we should not perform this lossy conversion if the top level call to the pretty-printer was
1386 /// done for a token stream or a single token.
1387 pub struct IdentPrinter {
1390 /// Span used for retrieving the crate name to which `$crate` refers to,
1391 /// if this field is `None` then the `$crate` conversion doesn't happen.
1392 convert_dollar_crate: Option<Span>,
1396 /// The most general `IdentPrinter` constructor. Do not use this.
1397 pub fn new(symbol: Symbol, is_raw: bool, convert_dollar_crate: Option<Span>) -> IdentPrinter {
1398 IdentPrinter { symbol, is_raw, convert_dollar_crate }
1401 /// This implementation is supposed to be used when printing identifiers
1402 /// as a part of pretty-printing for larger AST pieces.
1403 /// Do not use this either.
1404 pub fn for_ast_ident(ident: Ident, is_raw: bool) -> IdentPrinter {
1405 IdentPrinter::new(ident.name, is_raw, Some(ident.span))
1409 impl fmt::Display for IdentPrinter {
1410 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1413 } else if self.symbol == kw::DollarCrate {
1414 if let Some(span) = self.convert_dollar_crate {
1415 let converted = span.ctxt().dollar_crate_name();
1416 if !converted.is_path_segment_keyword() {
1419 return fmt::Display::fmt(&converted, f);
1422 fmt::Display::fmt(&self.symbol, f)
1426 /// An newtype around `Ident` that calls [Ident::normalize_to_macro_rules] on
1428 // FIXME(matthewj, petrochenkov) Use this more often, add a similar
1429 // `ModernIdent` struct and use that as well.
1430 #[derive(Copy, Clone, Eq, PartialEq, Hash)]
1431 pub struct MacroRulesNormalizedIdent(Ident);
1433 impl MacroRulesNormalizedIdent {
1434 pub fn new(ident: Ident) -> Self {
1435 Self(ident.normalize_to_macro_rules())
1439 impl fmt::Debug for MacroRulesNormalizedIdent {
1440 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1441 fmt::Debug::fmt(&self.0, f)
1445 impl fmt::Display for MacroRulesNormalizedIdent {
1446 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1447 fmt::Display::fmt(&self.0, f)
1451 /// An interned string.
1453 /// Internally, a `Symbol` is implemented as an index, and all operations
1454 /// (including hashing, equality, and ordering) operate on that index. The use
1455 /// of `rustc_index::newtype_index!` means that `Option<Symbol>` only takes up 4 bytes,
1456 /// because `rustc_index::newtype_index!` reserves the last 256 values for tagging purposes.
1458 /// Note that `Symbol` cannot directly be a `rustc_index::newtype_index!` because it
1459 /// implements `fmt::Debug`, `Encodable`, and `Decodable` in special ways.
1460 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
1461 pub struct Symbol(SymbolIndex);
1463 rustc_index::newtype_index! {
1464 pub struct SymbolIndex { .. }
1468 const fn new(n: u32) -> Self {
1469 Symbol(SymbolIndex::from_u32(n))
1472 /// Maps a string to its interned representation.
1473 pub fn intern(string: &str) -> Self {
1474 with_interner(|interner| interner.intern(string))
1477 /// Convert to a `SymbolStr`. This is a slowish operation because it
1478 /// requires locking the symbol interner.
1479 pub fn as_str(self) -> SymbolStr {
1480 with_interner(|interner| unsafe {
1481 SymbolStr { string: std::mem::transmute::<&str, &str>(interner.get(self)) }
1485 pub fn as_u32(self) -> u32 {
1489 pub fn is_empty(self) -> bool {
1493 /// This method is supposed to be used in error messages, so it's expected to be
1494 /// identical to printing the original identifier token written in source code
1495 /// (`token_to_string`, `Ident::to_string`), except that symbols don't keep the rawness flag
1496 /// or edition, so we have to guess the rawness using the global edition.
1497 pub fn to_ident_string(self) -> String {
1498 Ident::with_dummy_span(self).to_string()
1502 impl fmt::Debug for Symbol {
1503 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1504 fmt::Debug::fmt(&self.as_str(), f)
1508 impl fmt::Display for Symbol {
1509 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1510 fmt::Display::fmt(&self.as_str(), f)
1514 impl<S: Encoder> Encodable<S> for Symbol {
1515 fn encode(&self, s: &mut S) -> Result<(), S::Error> {
1516 s.emit_str(&self.as_str())
1520 impl<D: Decoder> Decodable<D> for Symbol {
1522 fn decode(d: &mut D) -> Result<Symbol, D::Error> {
1523 Ok(Symbol::intern(&d.read_str()?))
1527 impl<CTX> HashStable<CTX> for Symbol {
1529 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
1530 self.as_str().hash_stable(hcx, hasher);
1534 impl<CTX> ToStableHashKey<CTX> for Symbol {
1535 type KeyType = SymbolStr;
1538 fn to_stable_hash_key(&self, _: &CTX) -> SymbolStr {
1543 // The `&'static str`s in this type actually point into the arena.
1545 // The `FxHashMap`+`Vec` pair could be replaced by `FxIndexSet`, but #75278
1546 // found that to regress performance up to 2% in some cases. This might be
1547 // revisited after further improvements to `indexmap`.
1549 pub struct Interner {
1550 arena: DroplessArena,
1551 names: FxHashMap<&'static str, Symbol>,
1552 strings: Vec<&'static str>,
1556 fn prefill(init: &[&'static str]) -> Self {
1558 strings: init.into(),
1559 names: init.iter().copied().zip((0..).map(Symbol::new)).collect(),
1560 ..Default::default()
1565 pub fn intern(&mut self, string: &str) -> Symbol {
1566 if let Some(&name) = self.names.get(string) {
1570 let name = Symbol::new(self.strings.len() as u32);
1572 // `from_utf8_unchecked` is safe since we just allocated a `&str` which is known to be
1575 unsafe { str::from_utf8_unchecked(self.arena.alloc_slice(string.as_bytes())) };
1576 // It is safe to extend the arena allocation to `'static` because we only access
1577 // these while the arena is still alive.
1578 let string: &'static str = unsafe { &*(string as *const str) };
1579 self.strings.push(string);
1580 self.names.insert(string, name);
1584 // Get the symbol as a string. `Symbol::as_str()` should be used in
1585 // preference to this function.
1586 pub fn get(&self, symbol: Symbol) -> &str {
1587 self.strings[symbol.0.as_usize()]
1591 // This module has a very short name because it's used a lot.
1592 /// This module contains all the defined keyword `Symbol`s.
1594 /// Given that `kw` is imported, use them like `kw::keyword_name`.
1595 /// For example `kw::Loop` or `kw::Break`.
1597 pub use super::kw_generated::*;
1600 // This module has a very short name because it's used a lot.
1601 /// This module contains all the defined non-keyword `Symbol`s.
1603 /// Given that `sym` is imported, use them like `sym::symbol_name`.
1604 /// For example `sym::rustfmt` or `sym::u8`.
1607 use std::convert::TryInto;
1610 pub use super::sym_generated::*;
1612 // Used from a macro in `librustc_feature/accepted.rs`
1613 pub use super::kw::MacroRules as macro_rules;
1615 /// Get the symbol for an integer.
1617 /// The first few non-negative integers each have a static symbol and therefore
1619 pub fn integer<N: TryInto<usize> + Copy + ToString>(n: N) -> Symbol {
1620 if let Result::Ok(idx) = n.try_into() {
1622 return Symbol::new(super::SYMBOL_DIGITS_BASE + idx as u32);
1625 Symbol::intern(&n.to_string())
1630 fn is_special(self) -> bool {
1631 self <= kw::Underscore
1634 fn is_used_keyword_always(self) -> bool {
1635 self >= kw::As && self <= kw::While
1638 fn is_used_keyword_conditional(self, edition: impl FnOnce() -> Edition) -> bool {
1639 (self >= kw::Async && self <= kw::Dyn) && edition() >= Edition::Edition2018
1642 fn is_unused_keyword_always(self) -> bool {
1643 self >= kw::Abstract && self <= kw::Yield
1646 fn is_unused_keyword_conditional(self, edition: impl FnOnce() -> Edition) -> bool {
1647 self == kw::Try && edition() >= Edition::Edition2018
1650 pub fn is_reserved(self, edition: impl Copy + FnOnce() -> Edition) -> bool {
1652 || self.is_used_keyword_always()
1653 || self.is_unused_keyword_always()
1654 || self.is_used_keyword_conditional(edition)
1655 || self.is_unused_keyword_conditional(edition)
1658 /// A keyword or reserved identifier that can be used as a path segment.
1659 pub fn is_path_segment_keyword(self) -> bool {
1661 || self == kw::SelfLower
1662 || self == kw::SelfUpper
1663 || self == kw::Crate
1664 || self == kw::PathRoot
1665 || self == kw::DollarCrate
1668 /// Returns `true` if the symbol is `true` or `false`.
1669 pub fn is_bool_lit(self) -> bool {
1670 self == kw::True || self == kw::False
1673 /// Returns `true` if this symbol can be a raw identifier.
1674 pub fn can_be_raw(self) -> bool {
1675 self != kw::Empty && self != kw::Underscore && !self.is_path_segment_keyword()
1680 // Returns `true` for reserved identifiers used internally for elided lifetimes,
1681 // unnamed method parameters, crate root module, error recovery etc.
1682 pub fn is_special(self) -> bool {
1683 self.name.is_special()
1686 /// Returns `true` if the token is a keyword used in the language.
1687 pub fn is_used_keyword(self) -> bool {
1688 // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1689 self.name.is_used_keyword_always()
1690 || self.name.is_used_keyword_conditional(|| self.span.edition())
1693 /// Returns `true` if the token is a keyword reserved for possible future use.
1694 pub fn is_unused_keyword(self) -> bool {
1695 // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1696 self.name.is_unused_keyword_always()
1697 || self.name.is_unused_keyword_conditional(|| self.span.edition())
1700 /// Returns `true` if the token is either a special identifier or a keyword.
1701 pub fn is_reserved(self) -> bool {
1702 // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1703 self.name.is_reserved(|| self.span.edition())
1706 /// A keyword or reserved identifier that can be used as a path segment.
1707 pub fn is_path_segment_keyword(self) -> bool {
1708 self.name.is_path_segment_keyword()
1711 /// We see this identifier in a normal identifier position, like variable name or a type.
1712 /// How was it written originally? Did it use the raw form? Let's try to guess.
1713 pub fn is_raw_guess(self) -> bool {
1714 self.name.can_be_raw() && self.is_reserved()
1719 fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
1720 SESSION_GLOBALS.with(|session_globals| f(&mut *session_globals.symbol_interner.lock()))
1723 /// An alternative to [`Symbol`], useful when the chars within the symbol need to
1724 /// be accessed. It deliberately has limited functionality and should only be
1725 /// used for temporary values.
1727 /// Because the interner outlives any thread which uses this type, we can
1728 /// safely treat `string` which points to interner data, as an immortal string,
1729 /// as long as this type never crosses between threads.
1731 // FIXME: ensure that the interner outlives any thread which uses `SymbolStr`,
1732 // by creating a new thread right after constructing the interner.
1733 #[derive(Clone, Eq, PartialOrd, Ord)]
1734 pub struct SymbolStr {
1735 string: &'static str,
1738 // This impl allows a `SymbolStr` to be directly equated with a `String` or
1740 impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for SymbolStr {
1741 fn eq(&self, other: &T) -> bool {
1742 self.string == other.deref()
1746 impl !Send for SymbolStr {}
1747 impl !Sync for SymbolStr {}
1749 /// This impl means that if `ss` is a `SymbolStr`:
1750 /// - `*ss` is a `str`;
1751 /// - `&*ss` is a `&str` (and `match &*ss { ... }` is a common pattern).
1752 /// - `&ss as &str` is a `&str`, which means that `&ss` can be passed to a
1753 /// function expecting a `&str`.
1754 impl std::ops::Deref for SymbolStr {
1757 fn deref(&self) -> &str {
1762 impl fmt::Debug for SymbolStr {
1763 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1764 fmt::Debug::fmt(self.string, f)
1768 impl fmt::Display for SymbolStr {
1769 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1770 fmt::Display::fmt(self.string, f)
1774 impl<CTX> HashStable<CTX> for SymbolStr {
1776 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
1777 self.string.hash_stable(hcx, hasher)
1781 impl<CTX> ToStableHashKey<CTX> for SymbolStr {
1782 type KeyType = SymbolStr;
1785 fn to_stable_hash_key(&self, _: &CTX) -> SymbolStr {